Applied Physics Seminar: GaAsNBi: A Magic Alloy with Promise for Concentrating Photovoltaics

Due to their significant bandgap narrowing, dilute nitride alloys are promising for concentrating photovoltaics expected to power the next generation. However, N-related point defects often lead to degraded minority carrier transport properties and optical efficiencies. For example, in GaAsN, it has been suggested that N shares an arsenic site with either arsenic or another N atom, often termed (N-As)As or (N-N)As split interstitials. , Co-alloying of GaAsN with larger elements, such as indium, antimony, and/or bismuth, allows lattice-matching to GaAs or Ge substrates. Of particular interest is GaAsNBi, which is expected to provide the largest bandgap reductions, with tunable valence band and spin-orbit energy level splittings that are promising for temperature-insensitive lasers, high selectivity spin valves, and topological Dirac semimetals. In this talk, we discuss molecular-beam epitaxy of GaAsNBi alloys, identifying arsenic tetramer-enhanced bismuth incorporation and bismuth-flux enhanced nitrogen incorporation. We describe our combined computational-experimental ion beam studies which reveal bismuth and nitrogen substitutions for arsenic, along with nitrogen-arsenic pair formation at arsenic dangling bonds. Finally, we discuss our discovery of the “magic” bismuth to nitrogen ratio needed for lattice-matching to GaAs, our observations of surface-reconstruction-dependent atomic ordering of the alloys, and on-going measurements of the optoelectronic properties of alloy layers and quantum wells.
This work was supported by the National Science Foundation (DMR 1410282 & DMR 1810280), the Center for Integrated Nanotechnologies (CINT), jointly operated by Los Alamos and Sandia National Laboratories for the U.S. Department of Energy (DoE), and the Office of Science Graduate Student Research Program, administered by the Oak Ridge Institute for Science and Education for the U.S. DoE.
Brief Biography: Rachel S. Goldman is a professor of MSE, Physics, and EECS at UM. She is Associate Director of Applied Physics, and has served as Graduate Chair of MSE, Associate Director of the DoE Energy Frontiers Research Center, and Education Director of the NSF Materials Research Science and Engineering Center (MRSEC). Goldman received degrees from UM (B.S. Physics, 1988), Cornell (M.S. Applied Physics, 1992), and UC-San Diego (PhD Materials Science, 1995). Following her PhD, she was a postdoctoral fellow in Physics at Carnegie Mellon. In 1997, she joined the UM faculty as the Dow Corning Assistant Professor. She received the Peter Mark Memorial Award (AVS, 2002), the Ted Kennedy Family Team Excellence Award (UM, 2004), the Augustus Anson Whitney Fellowship (Harvard, 2005), and the Monroe-Brown Foundation Service Excellence Award (UM, 2011). Goldman was elected Fellow of APS and AVS in 2012, and received the Distinguished Faculty Achievement Award (UM, 2016) and the Raymond J. and Monica E. Schultz Outreach and Diversity Award (UM, 2019). Goldman has Chaired the Electronic Materials Division of AVS; she has also served on the AVS Board of Directors and as an AVS Trustee. She has served as Associate Editor of Journal of Electronic Materials and Journal of Vacuum Science and Technology; she is currently Associate Editor of the Journal of Applied Physics. Goldman has served on the DoE BES Committee of Visitors and is currently a member of the Scientific Advisory Committee for CINT.

. M. Reason, H. McKay, W. Ye, S. Hanson, V. Rotberg, R.S. Goldman, Appl. Phys. Lett. 85, 1692 (2004).
. T. Jen, G. Vardar, Y.Q. Wang, and R.S. Goldman, Appl. Phys. Lett. 107, 221904 (2015).
. R.L. Field III, J. Occena, T. Jen, D. DelGaudio, B. Yarlagadda, C. Kurdak, R.S. Goldman, Appl. Phys. Lett. 109, 252105 (2016).
. J.C. Occena, T. Jen, E.E. Rizzi, T.M. Johnson, J. Horwath, Y.Q. Wang, R.S. Goldman, Appl. Phys. Lett. 110, 242102 (2017).
. J. Occena, T. Jen, B. A. Carter, T. S. Jimson, A. G. Norman, R. S. Goldman, "Surfactant-induced Chemical Ordering of GaAsN:Bi," Appl. Phys. Lett. 113, 211602 (2018).